1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive sheet.
2. Description of the Related Art
A pressure-sensitive adhesive sheet is used for adhering adherends to each other or for fixing an article to an adherend by being firmly adhered to the adherend. The properties required of the pressure-sensitive adhesive sheet are various depending on applications, and for example, in order to prevent a decrease in yield caused by an attachment mistake, there is a need for a pressure-sensitive adhesive sheet in which reattachment (reworkability) is taken into consideration. That is, there is a need for a pressure-sensitive adhesive sheet that exhibits low pressure-sensitive adhesive force at the beginning of attachment and high pressure-sensitive adhesive force when an adherend is used.
In order to meet such a change in pressure-sensitive adhesive force, methods for changing the pressure-sensitive adhesive force of pressure-sensitive adhesive sheets by heating or ultraviolet radiation have traditionally been used (see Patent Documents 1 to 4).
[PATENT DOCUMENT 1] Japanese Patent Application Publication No. Hei 11-302610
[PATENT DOCUMENT 2] Japanese Patent Application Publication No. Hei 11-302614
[PATENT DOCUMENT 3] Japanese Patent Application Publication No. 2011-127054
[PATENT DOCUMENT 4] Japanese Patent Application Publication No. 2007-045974
Even with the same pressure-sensitive adhesive sheet, pressure-sensitive adhesive properties may be different when the material of an adherend is different. Additionally, reattachment may be required immediately after a pressure-sensitive adhesive sheet is attached to an adherend, or reattachment may be required after some time has passed since it was attached, depending on the application of the sheet.
However, the pressure-sensitive adhesive sheet described in each of Patent Documents 1 to 4 increases pressure-sensitive adhesive force over time, although exhibits low pressure-sensitive adhesive force at the beginning of attachment. Accordingly, when the elapsed time between the attachment of a pressure-sensitive adhesive sheet to an adherend and the reattachment of the sheet is long, there is room for an improvement in reworkability.